Glass tube assemblies as described in the present application in which a glass tube or glass rod spiral is mounted inside a glass tube, are used in many various forms in heat exchangers and in the process treatment of gas flows, for example in the recovery of strong acids, such as sulphuric acid, as described, for instance in the European patent application EP 0 687 658 A1 or in the U.S. Pat. No. 6,340,414 B1, the content of which is hereby expressly included by way of reference, in so far as this concerns potential applications of the invention claimed.
It is often necessary to cool down hot acidic gas flows in the end stage of such a process. This is done using a condenser assembly comprising a jacket tube and a spiral tube arranged inside the jacket tube. The spiral offers a large surface area and simultaneously ensures swirl mixing of the gas flowing through the jacket tube. This is used to condense out acid compounds or inorganic acids which are then recovered. The condensed acid compounds or acids, which condense onto the spiral tube, flow down inside the jacket tube following gravity and are collected in a collecting container.
U.S. Pat. No. 5,639,288 discloses a method for fixing the spiral tube in the jacket tube in which a thin glass tube is introduced into the jacket tube with a greater internal diameter via a guide tube mounted on the inside of the jacket tube. The guide tube is located in a heated area within the jacket tube in which the inserted glass tube is heated to its softening temperature. The guide tube has a curved outlet, so that glass tube continuously introduced into the guide tube and the heated zone is deformed into a spiral. Rotating the jacket tube causes the glass tube, which is given a spiral form in this way, to attach itself in a spiral form to the inner face of the jacket tube. Because the glass tube is heated to its softening point, a material bond is created between the jacket tube and the glass tube spiral.
It is indeed true that the location of the glass tube spiral can be reliably fixed by this method. A simple location of the glass tube spiral against axial longitudinal displacement in only one direction would, however, be sufficient for applications of the type described above in which the jacket tube is usually arranged vertically. The method overall is comparatively complex and does not permit reworking in the event of irregular arrangement of the glass tube spiral or other deviations from the desired configuration.
A circumferential taper at the lower end of the outer may also be used to secure the glass tube spiral against axial longitudinal displacement in a glass tube, although this has the undesirable effect of impairing the gas flow and the drainage of the condensate into the collecting container.
Alternatively, the use of stainless steel spiral tubes which are suspended in the vertically arranged outer glass tube is known from the prior art. However, when highly acid gas flows are being treated, the stainless steel and the material suspending the stainless steel spiral corrodes, considerably reducing the efficiency of treatment of the gas flow.